"No Trespassing"... it's that simple, stay out, no admittance, no hunting, no fishing, go away. 

The rule was added to Texas law in 1997 as an additional way to identify private property and warn people they are not to trespass. The law has recently been in force in Arkansas since 1989 and has been added to Louisiana as of May of 2018. There are at least 9 other states that use the Purple Paint Law as well, including Kansas, Arizona, Montana, Idaho, Florida, Maine, North Carolina, Missouri and Illinois.

There may be slight variations for other states so if you plan on hiking or hunting in the great outdoors you better know before you go just to make sure. However, it's probably safe to assume that if you see purple paint on a fence post, it's probably a good idea to stay off that piece of land.

Below is a good video explaining the law in Texas: